1. Field of the Invention
The present invention relates to a method and an apparatus for the purification of chlorosilane, a raw material of high purity polysilicon, and more particularly, to a method and an apparatus for the purification of chlorosilane, which are economical and have low energy consumption, as compared to the related art.
2. Description of the Related Art
In general, polysilicon, used as a raw material of a semiconductor or a solar battery, has been mainly manufactured by a vapor deposition method referred to as the Siemens method. In FIG. 1, a process of manufacturing polysilicon by the Siemens method according to the related art is schematically illustrated.
The process of manufacturing polysilicon may largely include an operation of fabricating trichlorosilane, a raw material thereof, an operation of purifying trichlorosilane to have a high level of purity, and an operation of reacting the purified trichlorosilane with hydrogen to generate polysilicon.
Referring to FIG. 1, the process of manufacturing polysilicon is explained in detail. First, metallic silicon 21, a raw material of polysilicon, and hydrochloric acid gas 22 are supplied to a reactor 101 and reacted with each other at a reaction temperature of 300 to 400° C., to thereby fabricate trichlorosilane. In this case, reaction products of the reaction of the metallic silicon and the hydrochloric acid gas may include hydrogen gas, unreacted hydrochloric acid gas, chlorosilanes, such as tetrachlorosilane, dichlorosilane, and the like mixed therein, as well as trichlorosilane, a target product.
Thus, the purification process for separating trichlorosilane, a target product, from the reaction products, may be performed. In general, in order to form high purity polysilicon, trichlorosilane having a purity of 99.9999999% to 99.999999999% is required. In order to obtain such a high purity trichlorosilane, the purification process may be generally undertaken through a plurality of purification towers. The purification process of trichlorosilane is hereinafter explained in detail.
First, in a pretreatment tower 102, a chlorosilane mixture is separated from the reaction products discharged from the reactor 101 through distillation. In this case, among the reaction products, hydrogen gas, hydrochloric acid gas, dichlorosilane, and the like, having a low boiling point, are discharged through a top stream 41 of the pretreatment tower 102, while the chlorosilane mixture including trichlorosilane and tetrachlorosilane, having a high boiling point, as main ingredients, is discharged through a bottom stream 42 of the pretreatment tower 102.
The bottom stream 42 of the pretreatment tower 102 is introduced to a first purification tower 103, and the chlorosilane mixture is separated into trichlorosilane and tetrachlorosilane through distillation in the first purification tower 103. In the chlorosilane mixture, trichlorosilane having a relatively low boiling point is discharged through a top stream 43, while tetrachlorosilane having a relatively high boiling point is discharged through a bottom stream 44. In this case, trichlorosilane discharged through the top stream 43 of the first purification tower 103 may generally have a purity of approximately 99%. However, as described above, since trichlorosilane having purity of 99.9999999% to 99.999999999% is generally required to produce high purity trichlorosilane, the top stream 43 of the first purification tower 103 is introduced to a second purification tower 104 and re-purified therein.
The trichlorosilane introduced to the second purification tower 104 is separated into a mixture of low-boiling point impurities and trichlorosilane, and a mixture of high-boiling impurities, such as tetrachlorosilane and trichlorosilane. The mixture of low-boiling impurities and trichlorosilane is discharged through a top stream 45 and passes through a condenser 201 to be liquefied. A portion of the liquefied mixture reflows to the second purification tower 104 and the remainder thereof 47 is discharged. Meanwhile, the mixture of high-boiling point impurities and trichlorosilane is discharged through a bottom stream 48, and then re-heated through a reboiler 301 in the second purification tower 104. Then, a portion 49 of the re-heated mixture is recycled to the second purification tower 104, and the remainder thereof 50 is introduced to a third purification tower 105 to be purified again. In the third purification tower 105, the mixture of high-boiling point impurities and trichlorosilane is separated into high purity trichlorosilane and trichlorosilane including high-boiling point impurities. In this case, high purity trichlorosilane is discharged through a top stream 51, and liquefied in a condenser 202. Then, a portion 52 of the liquefied trichlorosilane reflows to the third purification tower 105, and the remainder 53 thereof is discharged to a storage tank 1 for trichlorosilane. Meanwhile, trichlorosilane including high-boiling point impurities is discharged through a bottom stream 54 and re-heated through a reboiler 302. Then, a portion 55 of the re-heated trichlorosilane is recycled to the third purification tower, and the remainder 56 thereof is discharged. FIG. 1 illustrates a purification operation reaching only to a third purification tower; however, further purification steps may be performed as needed.
Through such an operation, trichlorosilane stored in the storage tank 1 for trichlorosilane is supplied to a reducing furnace 106 in which polysilicon is generated, as a raw material, together with hydrogen gas 2.
In the case of the method of manufacturing polysilicon according to the related art, in order to obtain high purity trichlorosilane, passing trichlorosilane through a plurality of purification towers is required, and the inclusion of a condenser cooling a top stream and a reboiler re-heating a bottom stream for each purification tower is required. Due to these requirements, the amount of utilities required is increased, and production costs and energy consumption are increased, in a manufacturing process.
Therefore, a method of purifying trichlorosilane, capable of reducing energy consumption used in the purification operation of trichlorosilane and curtailing production costs, in consideration of environmental and economical aspects, has been demanded.